Determination of phthalate monoesters, in human breast milk by high-performance liquid chromatography/tandem mass spectrometry

Phthalate diesters (PDEs) are ubiquitous contaminants in our life. Phthalate monoesters (PMEs) and their glucuronide conjugates are common metabolites of PDEs, which are detectable in sera and urine of humans exposed to PDEs. In animal studies, some PDEs and PMEs are toxicants to the reproductive and developmental systems. Thus, studies about exposure to PDEs and PMEs in human fetus and infants are required. Breast milk is one of the most important resources of nutrition to infants. However, there is significant information about the concentrations of PMEs in human breast milk. We developed a method to determine PMEs in human breast milk by using a liquid chromatograph-tandem mass spectrometer. Breast milk was extracted with ethylacetate/cyclohexane under an acidic condition. The organic phase was dried under an N-2 stream and dissolved in an acetic ammonium buffer. The extract was processed using enzymatic deconjugation of the glucuronidase, followed by solid-phase purification to obtain a test solution. The recoveries and relative standard deviations of PMEs (5.0 ng/mL) fortified in consumer milk were satisfactory, which were 96.3 similar to 103% and less than 5%, respectively. Eleven human milk samples obtained from Japanese women were examined. Monoethylphthalate (median; range, 0.5; 0.3 similar to 1.3 ng/mL), monobutylphthalate (26.0; 1.8 similar to 156), monobenzylphthalate (1.0; 0.7 similar to 74.3), monoethylhexylphthalate (27.9; 4.4 similar to 129) and monoisononylphthalate (1.2; 0.7 similar to 8.7) were detected from all of the samples. This method would be useful for the determination of PMEs in human breast milk.